1) Field of the Invention
The present invention relates to an optical switch, and in particular, the invention relates to an optical switch suitable for use as a wavelength-selective switch applied to an optical add/drop unit in a optical communication system.
2) Description of the Related Art
Recently, due to flexibility and high redundancy of communication networks, wavelength multiplex OADM (Optical Add Drop Multiplexer) devices are increasingly introduced commercially. Wavelength multiplex OADM devices require a function of switches freely arbitrary wavelengths to arbitrary paths in a network having a form of a ring or the like.
In particular, since a high-speed redundant function, such as switching a path at the time of break of a transmission path fiber, influences the reliability of the whole system, not only switching speed but also accuracy is necessary.
FIG. 19 shows an example of a construction of wavelength multiplex OADM node. A wavelength multiplex OADM (OADM device) 100 includes: a pre-amplifier 101; a splitter unit 102 which splits light from the pre-amplifier 101 into two; an wavelength-selective optical switch 103 for dropping which selectively drops light of an arbitrary wavelength channel of one of the light beams having been split by the splitter unit 102; an wavelength-selective optical switch 104 for adding which inserts light of a wavelength channel for add of the other light beam having been split by the splitter unit 102; and a post-amplifier 105.
Further, as shown in FIG. 19, the wavelength-selective switches 103 and 104, which are for drop and add, respectively, are constructed in such a manner that multiple wavelength-selective optical switches in a cascade form. Accordingly, since the wavelength multiplex OADM 100 having the construction shown in FIG. 19 has advantages that the load, such as work of adding of channels corresponding to the number of wavelengths and port connection work, etc., is small, it is considered that it will become one of the main streams of node constructions in wavelength multiplexing optical transmission systems from then on.
FIG. 20 and FIG. 21 show examples of an abbreviated construction of the wavelength selective optical switch 110 (103 and 104) for use in add and drop in the above-described wavelength multiplex OADM 100. FIG. 20 is an upper view of the diagrammatic construction of the wavelength-selective optical switch 110 (103 and 104) which is used for add and drop, and FIG. 21 is an front view. Here, the wavelength-selective optical switch 110 includes: collimators 111 which attempt to performing optical coupling between input and output optical fiber, which function as transmission paths; an optical splitter element 112 which splits parallel light from the collimator 111; a light-gathering lens 113; and a movable mirror array 114. Here, although the construction example shows that the input port 1 corresponds to the output port 2, input and output paths can be inverted and the output port 1 can correspond to the input port 2.
In the movable mirror array 114, mirror devices 114a are arranged in a form of an array (here, one row along with the X axis) so that reflection surface angles with respect to the X axis are individually set for mirror light (here, λ1 through λ5) split by the optical splitter element 112. In this instance, each mirror device 114a is supported in such a manner that it is individually rotatable with respect to the X axis and the Y axis. By means of a force received from a non-illustrated mechanism supplying physical external forces, such as mechanical, opto-electrical, or opto-magnetical effect, it is possible to individually set the reflect surface angles with respect to the X axis and the Y axis.
That is, by means of adjusting the reflection surface angle with respect to the X axis for each wavelength of the movable mirror array 114 of the light input through the collimator 111-1 in FIG. 21, it becomes possible to introduce reflected light to an output optical fiber through an arbitrary one of the two collimators 111-2 and 111-3. Hereby, a function of wavelength-selective switch which switches light input through an input 1 port to an output 2 port according to the wavelength channels, are realized. In this manner, the movable mirror arrays 114 of the number of wavelengths necessary for the optical transmission system are arranged, and each is adapted to individually moved.
Like the wavelength multiplex OADM 100 in FIG. 19, an ODAM device using a wavelength selective switch is designed to be upgraded to have several tens of channels in consideration to increase in traffic in future in the optical transmission system. Normally, when the system is initially introduced, service generally starts with a small number of channels. In this case, the number of channels not in operation is relatively large.
Such standby channels not in operation, that is, not in service are shuttered in a shutter movement region in an optical switch to remove natural radiation light (ASE light) by an optical amplifier arranged in an optical transmission path, and to prevent the occurrences of optical surges in an optical amplifier due to abrupt light input. More specifically, as shown in FIG. 22, the reflect surface angles of the mirror devices 114a can be set with respect to not only the X axis but the Y axis. Thus, light in channels not in operation is introduced to a region St (Shutter movement region) which is deviated from a region optically coupled to the collimators 111-2 and 111-3 which are output destination (see return light indicated by the broken line in FIG. 22).
In this instance, as technology relating to wavelength-selective optical switches, the following patent documents 1 and 2, for example, exist. In addition, as technology relating to the present invention, the following patent documents 3 and 4 exist.
[Patent Document 1] U.S. Pat. No. 6,661,948
[Patent Document 2] Japanese Patent Application Laid-Open No. 2006-276487
[Patent Document 3] Japanese Patent Application Laid-Open No. 2003-215645
[Patent Document 4] Japanese Patent Application Laid-Open No. HEI 2-024635
The reflection surface angle of the movable mirror array 114 included in the above-described optical switch 110 shown in the above-described FIG. 20 and FIG. 21, is variably changed in response to a physical external force such as mechanical, opto-electrical, or opto-magnetic one, and there exists a certain disorder occurrence rate. On the other hand, when the optical switch 110 is applied to the above-described wavelength multiplex OADM 100 or the like, the above-described redundant operation such as path switching is performed. At that time, standby optical ports and wavelength channels need to be switched in high-speed at the time of occurrence of disorder.
Hence, when a wavelength-selective optical switch is applied to a wavelength multiplex OADM device 100 or the like, as preventive measures at the time of the above-mentioned occurrence of disorder, the optical switch itself is desirable to supervise that it has sufficient switching ability even during standby (that is, at the time not in operation), and also to always perform detect ion of disorders.
However, in the optical switch 110 shown in FIG. 20 and FIG. 21, as shown in FIG. 22, as to light of wavelength channels not in operation is not positively coupled to the collimators 111-2 and 111-3, which are output destination, and thus, the optical switch 110 never output an optical signal outside the optical switch. In consequence, there is an issue that it is impossible to observe from outside the presence and the absence of input of a signal light of standby channels, disorder of standby channels, deterioration of the movable mirror array 114 or the like.
None of the above patent documents 1 through 4 does not disclose technology for supervising the performance of optical switching in the above-described standby channels.